Bryant 548D - Manual (Page 10)

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LEGEND AND NOTES FOR TABLES 2A AND 2B
LEGEND
*Heaters are field installed only.
†Used to determine minimum disconnect per NEC.
**Heater capacity (kW) is based on heater voltage of 208 v, 240 v, or 480 v and
575 v. If power distribution voltage to unit varies from rated heater voltage,
heater kW will vary accordingly.
††Fuse or HACR circuit breaker.
||Optional disconnect switch is unavailable. (Applies to units with an FLA greater
or equal to 80.)
NOTES:
1. In compliance with NEC requirements for multimotor and combination load
equipment (refer to NEC Articles 430 and 440), the overcurrent protective
device for the unit shall be fuse or HACR breaker.
2. Unbalanced 3-Phase Supply Voltage
Never operate a motor where a phase imbalance in supply voltage is greater
than 2%. Use the following formula to determine the percentage of voltage
imbalance.
% Voltage Imbalance
Example: Supply voltage is 460-3-60.
AB = 452 v
BC = 464 v
AC = 455 v
= 457
Determine maximum deviation from average voltage.
(AB) 457 – 452 = 5 v
(BC) 464 – 457 = 7 v
(AC) 457 – 455 = 2 v
Maximum deviation is 7 v.
Determine percent of voltage imbalance.
= 1.53%
This amount of phase imbalance is satisfactory as it is below the maximum
allowable 2%.
IMPORTANT: If the supply voltage phase imbalance is more than 2%, con-
tact your local electric utility company immediately.
FLA — Full Load Amps
HACR — Heating, Air Conditioning and Refrigeration
IFM — Indoor-Fan Motor
LRA — Locked Rotor Amps
MCA — Minimum Circuit Amps
MOCP — Maximum Overcurrent Protection
NEC — National Electrical Code
OFM — Outdoor-Fan Motor
RLA — Rated Load Amps
= 100 x
max voltage deviation from average voltage
average voltage
Average Voltage =
452 + 464 + 455
3
=
1371
3
% Voltage Imbalance = 100 x
7
457